Python Manual Index

It searches for keywords in the Python manuals at
http://www.python.org/doc/.
The advantage over pydoc is that it also
looks in the C-api manual, which you need when you are writing extension modules.

The script can also be downloaded, and can be configured to search HTML manual
pages installed locally. The keyword index is build on the fly.
It can also (probably) be easily integrated in your editor/ide to provide
context sensitive help.